The conditions of acceptance of no-difference findings are especially critical in mental and physical health research since we are in a period of fiscal austerity when the non-usefulness of existing programs is open to question. Also, systematic progress in any field will inevitably bring researchers closer to the no-difference case as new standards of attainment are developed. The tentative categorization of these conditions presented in this proposal would be further developed and refined through a thorough search of the literature and an analysis of conditions related to findings of no difference. Those conditions judged to be most important in understanding no-difference findings would be empirically validated by systematically varying simulated descriptions of findings given to experts in mental and physical health and research design and evaluation. Finally, a set of interpretative guidelines useful to researchers and another set of guidelines useful to research consumers (e.g., administrators, practitioners) will be developed and field tested using the results of the literature search and experiment study. The research should add to the conceptual understanding of no-difference findings and increase the inferential quality of studies in mental and physical health.